widl: added dispinterface and coclass

[Mike Hearn]

Jacek Caban wrote:
> Changelog:
>   - Added creation of dispinterface header
>   - Added creation of coclass header
>   - Added messages when fopen failes

Cool! How far away are we from having widl generate the proxy/stub 
marshalling code? I started writing some COM test cases last night but 
it's really hard to test anything non-trivial without a test object that 
supports marshalling and I doubt Alexandre would want MIDL code in the 
test suite (or maybe he would, that is what we have to run after all ...)

thanks -mike